Apparatus and method for rubbing LCD substrate

ABSTRACT

The invention provides an apparatus and a method for rubbing the alignment layer in the LCD substrate. The rubbing apparatus of the present invention further includes a second rolling apparatus for conditioning, in addition to the first rolling apparatus for rubbing, to rejuvenate the first rolling apparatus in real time so as to lengthen the lifetime of the rolling apparatus in the rubbing process and increase the rubbing rate. By employing the second rolling apparatus along with the first rolling apparatus, the rubbing process includes an extra conditioning step for conditioning the first rolling apparatus, thus shortening the production cycle time and increasing the throughput.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of, and claims the prioritybenefit of, U.S. application Ser. No. 10/936,923 filed on Sep. 8, 2004,which is a continuation of a prior application Ser. No. 10/065,976,filed Dec. 5, 2002 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to an apparatus and a method for rubbingliquid crystal display (LCD) substrates. More particularly, the presentinvention relates to an apparatus and a method for rubbing the alignmentlayer in the LCD substrate.

2. Description of Related Art

The cathode ray tube (CRT) has dominated our desktops and living roomsfor half a century as the standard display for monitors. However, theCRT is now facing real competition in the form of monitors or displaypanels based on liquid crystal displays (LCDs).

Most of the LCD devices using electro-optical effects of liquid crystalsas a light modulator, such as the twisted nematic (TN)-effect and thein-plane switching (IPS)-effect for thin film transistor liquid crystaldisplays (TFT LCDs). The most common LCD in use today is TFT-LCD, havinga sandwich-like structure with liquid crystal filled between two glassplates.

The liquid crystal is the material that possesses properties of theliquid including fluidity and the solid including long-range order atthe same time. Liquid crystal molecules have unique structures in a barshape, and they have the anisotropic characteristics.

Liquid crystal displays in use rely on pixels formed by liquid-crystal(LC) cells that change the polarization direction of light passingthrough them in response to an electrical voltage. The polarizationorientation of the liquid crystal molecule is determined by the rubbingdirection of the alignment layer.

Rubbing process is commonly used by most LCD manufacturers to forms thestraight groove in a fixed direction on the hardened alignment layer, sothat the liquid crystal molecules can align in the fixed direction. Therubbing process is performed through mechanical contact between therubbing roller and the alignment layer. However, if the rubbing rollerdegrades unexpectedly or unevenly, the effect of a local defect on thealignment layer may not be detected until hundreds of flawed displayshave been manufactured and subsequently discarded. Moreover, rubbingrate is deferred to a large extent by the poor conditions orinstabilities of the rubbing roller. Therefore, it is in great demand toimprove the rubbing roller or the present rubbing process, in order toincrease reliability and enhance rubbing performance.

SUMMARY OF THE INVENTION

The invention provides an apparatus and a method for rubbing thealignment layer in the LCD substrate.

The present invention provides a rubbing process involving an additionalconditioning step in the rubbing process to reduce rubbing defects andenhance the performance. The rubbing apparatus of the present inventionfurther includes a second rolling apparatus for conditioning, inaddition to the first rolling apparatus for rubbing, to rejuvenate thefirst rolling apparatus in real time so as to lengthen the lifetime ofthe first rolling apparatus in the rubbing process and increase therubbing rate.

Therefore, the present invention provides the first rolling apparatus incombination of the second rolling apparatus, in order to improve rubbingquality and enhance rubbing performance. By employing the second rollingapparatus for conditioning the first rolling apparatus, the rubbingprocess includes an extra conditioning step for revitalizing the firstrolling apparatus for rubbing. The conditioning step can lengthen thelifetime of the first rolling apparatus for rubbing, so that the firstrolling apparatus do not have to be replaced too often, thus shorteningthe production cycle time and increasing the throughput.

As embodied and broadly described herein, the invention provides arubbing apparatus, comprising: a platform, a conveyor, a based plate onthe conveyor, a first rolling apparatus having a rubbing cloth on itssurface above the base plate, a second rolling apparatus having aconditioning cloth on its surface aside to the first rolling apparatusand above the base plate. A plurality of first and second pile fibersare formed on surfaces of the rubbing cloth and the conditioning clothrespectively. The first rolling apparatus rotates in a first rotatingdirection opposite to a second rotating direction in which the secondrolling apparatus rotates, and a predetermined distance is arrangedbetween the first rolling apparatus and the second rolling apparatus, sothat the second pile fibers of the conditioning cloth on the secondrolling apparatus are in contact with the first pile fibers of therubbing cloth on the first rolling apparatus, thereby rejuvenating therubbing cloth on the first rolling apparatus.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings,

FIG. 1 shows the twisted structure of liquid crystal molecules in theliquid crystal layers;

FIG. 2A is a schematic, display view for illustrating the rubbingprocess;

FIG. 2B is a top view showing the moving direction and the rubbingdirection for the rubbing process; and

FIG. 3 is a schematic, display view for illustrating employing therubbing roller along with the conditioning roller in the rubbing processaccording to one preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Most LCDs, such as active-matrix LCD (AMLCD), currently on the marketbelong to the twisted nematic (TN) type that use linear polarizers totransmit or block light. Linear polarizers absorb (or block) light thatis not polarized exactly in their orientation and pass all light that isin their orientation.

For the liquid crystal layer in the twisted state with no electric fieldapplied, the light follows the twisted structure, resulting in arotation of 90 degrees. It is because nematic liquid crystals 100naturally order themselves in layers as shown in FIG. 1, the liquidcrystal layers (acting like polarizers) changes the polarization of thelight from axis A to axis B.

The twisted structure shown in FIG. 1 is created when liquid crystalmolecules in the liquid crystal layer are anchored (aligned) through arubbing process. Generally, the flow of the LCD process can be describedas follows: forming a alignment (orientation) layer on the lower and theupper plates respectively, positioning the alignment layer through therubbing process so as to properly align the liquid crystals on thealignment layer, dispensing the spacer and assembling the two plates andthen injecting the liquid crystal into the cell. A liquid crystaldisplay device is formed by interposing liquid crystal molecules betweena pair of substrate members, at least one of which transmits light. Thepair of substrate members is obtained by forming a display electrode ona light transmitting substrate and thereafter forming an alignment layeron the substrate that contains the electrode. The alignment layer has afunction of aligning the liquid crystal molecules in one direction. Toprovide for this function, a surface of the alignment film is rubbed bya rubbing apparatus.

In the rubbing process, straight grooves are formed in the alignmentlayer in a fixed direction, so that the liquid crystal molecules canalign in the pretilt direction. The rubbing process is performed throughmechanical contact between the rubbing roller and the alignment layer.FIG. 2A illustrates the general concept for the rubbing process. Therubbing process is performed to an alignment layer 202 coated on asurface of a LCD substrate 200. For example, a material of the alignmentlayer includes polyimide (PI) or poly amic acids (PA), while a materialfor the substrate comprises glass. In the rubbing process, the LCDsubstrate 200, which is mounted on a moving base plate 210, passes undera rubbing roller 204 and a rubbing cloth 206 coated on the rubbingroller 204 rubs the alignment layer 202. The rubbing roller 204 isusually a rotating drum made of aluminum and coated with the rubbingcloth 206. The base plate 210 is moved by an underlying conveyor (notshown). Several materials can be used to fabricate the rubbing cloth206, including rayon, cotton or nylon. The rubbing cloth is a clothsimilar to velvet, having a piled surface (i.e. having a lot of shortpile fibers). It is essential for the rubbing cloth to havehigh-density, uniform pile fibers on the surface, which are not easilyshed.

Rubbing the surface of the alignment layer provides the energy necessaryfor holding the liquid crystal in its twisted state, thus resulting inthe surface alignment of the liquid crystals along the rubbingdirection. The exaggerated lines shown in FIG. 2B represent the groovesformed by rubbing parallel to the (rubbing) direction A in which thealignment layer is rubbed. Without the effect of rubbing, the liquidcrystal molecules may reorient themselves in a random fashion, as shownin FIG. 2B left to the rubbing roller 204 (before rubbing).

Usually, there is a pretilt angle θ between the direction the alignmentlayer is rubbed (i.e. the rubbing direction) and the moving direction ofthe alignment layer. As shown in FIG. 2B, the pretilt angle θ betweenthe rubbing direction A and the moving direction B of the alignmentlayer is between 0–90 degrees, preferably about 45 degrees. Nonetheless,in an STN (super-twisted nematic) liquid crystal display device, forinstance, liquid crystal molecules are aligned as they are twisted inthe range of 180 degrees or larger, e.g., 210 to 260 degrees, betweenthe substrate members. The pretilt angle θ is adjustable dependent onthe materials of the alignment layers or product requirements. In therubbing process, many parameters have to be considered to control thepretilt angle and to determine the rubbing strength, including therubbing speed and the down force of the roller, the moving speed of thebase plate, rubbing times, and pile impression.

However, if the rubbing roller degrades unexpectedly or unevenly, itwill cause undesired defects in the alignment layer, thus leading toflawed display. Most often the deterioration of the rubbing roller comesfrom the rubbing cloth. That is, the pile on the surface of the rubbingcloth becomes pressed or deflated. In order to prevent local defects onthe alignment layer by the degraded roller, it is necessary torejuvenate or restore the rubbing roller before it deterioratesseverely.

Therefore, the present invention provides a rubbing process involving anadditional conditioning step in the rubbing process to enhance theperformance. The rubbing apparatus of the present invention furtherincludes a conditioning roller, in addition to the rubbing roller. FIG.3 illustrates the rubbing roller incorporating the conditioning rolleremploying in the rubbing process according to one preferred embodimentof the present invention.

The rubbing process is performed by pressing a cylindrical rubbingroller on the alignment layer on the substrate at a prescribed pressureand moving the substrate in a predetermined direction (i.e. the rubbingdirection), while rotating the rubbing roller. The rubbing process isperformed to a substrate 300 mounted on a moving base plate 310. Thebase plate 310 is disposed on a conveyor 312, while the conveyor 312 isarranged in a platform 320. In the platform 320, the base plate 310serves to carry the substrate 300 and the conveyor 312 arranged underthe base plate 310 serves to move the base plate 310. The conveyor 312can move the substrate 300 along the moving direction B to apredetermined location or levelly rotate the substrate 300 to adjust thepretilt angle. The substrate 300 includes an alignment layer 301.Various materials can be used to form the alignment layer for differentLCD substrates. The substrate 300, moving by the conveyor 312, movesunder a rubbing roller 302 coated with a rubbing cloth 306. As shown inFIG. 3, a conditioning roller 304 is arranged aside to the rubbingroller 302, so that the rubbing roller 302 is conditioned by contactingits surface with the conditioning roller 304. An exhaust cover plate 309is arranged under the conditioning roller 304 and above the substrate300, to prevent the conditioning roller 304 in contact with theunderlying substrate 300. The rubbing roller 302, the conditioningroller 304 and the exhaust cover plate 309 are connected to or fixed tothe platform 320. By employing the conditioning roller along with therubbing roller, the rubbing process includes an extra conditioning step.

The conditioning roller 304 is a powered rotating roller, rotating in adirection opposite to the rotating direction of the rubbing roller 302.That is, if the conditioning roller 304 rotates clockwise, the rubbingroller 302 rotates counter-clockwise, and vices versa. The rotatingspeeds of both the rubbing roller 302 and the conditioning roller 304can be adjusted, depending on the levels of conditioning. Preferably,the rotating speed of the conditioning roller 304 is faster than that ofthe rubbing roller 302. The conditioning roller 304 is similar to therubbing roller 302, a rotating drum made of aluminum and coated with aconditioning cloth 308. Likewise, several materials can be used tofabricate the conditioning cloth 308, including rayon, cotton or nylon,depending on the process requirements. The conditioning cloth is a clothsimilar to the rubbing cloth, having a piled surface (i.e. having a lotof short pile fibers). A predetermined distance is arranged between therubbing roller and the conditioning roller, so that the pile fibers onthe conditioning cloth are in touch with the pile fibers on the rubbingcloth. Because the conditioning roller 304 rotates in an oppositedirection to the rotating direction of the rubbing roller 302, theconditioning cloth 308 coated on the conditioning roller 304 canrejuvenate the surface of the rubbing cloth 306 on the rubbing roller302. Through pile contacts between the conditioning cloth and therubbing cloth, the pile on the surface of the rubbing cloth is reset (ortuned) to the original (desired) conditions.

The positions of both the conditioning and the rubbing rollers can beadjusted in order to change the distance between the conditioning rollerand the rubbing roller. The conditioning roller is either swept acrossthe surface of the rubbing roller in a controlled manner, or is ofsufficient dimension to condition the entire surface of the rubbingroller where it is in contact with the substrate. Conditioning may beperformed in situ (while the substrate is being rubbed), ex situ(between substrates), or combination of both. The manner in which therubbing roller is conditioned corresponds to the wear level of therubbing roller.

The present invention can further provides a liquid crystal display(LCD) device and a method for manufacturing the LCD device thereof byemploying the rubbing apparatus or the rubbing process of the presentinvention. Such LCD device comprising: a pair of substrate members, atleast either one of the pair of substrate members being capable oftransmitting light, and a liquid crystal disposed between the pair ofsubstrate members. At least either one of the substrate members includesan alignment layer which is rubbed using a rubbing apparatus comprising:a rubbing roller having a rubbing cloth on a surface of the rubbingroller, wherein a surface of the rubbing cloth has a plurality of firstpile fibers, wherein the rubbing roller to be moved together with thesubstrate member in relation to each other to thereby perform rubbing tothe alignment layer; and a conditioning roller arranged aside to therubbing roller, having a conditioning cloth on a surface of theconditioning roller, wherein a surface of the conditioning cloth has aplurality of second pile fibers. The rubbing roller rotates in a firstrotating direction opposite to a second rotating direction in which theconditioning roller rotates, and a predetermined distance is arrangedbetween the rubbing roller and the conditioning roller, so that thesecond pile fibers of the conditioning cloth on the conditioning rollerare in contact with the first pile fibers of the rubbing cloth on therubbing roller.

Generally, instabilities or deterioration in the rubbing roller directlyleads to poor rubbing performance or faulty rubbing. In this case,conditioning helps rejuvenating the rubbing roller, thus reducingrubbing defects and enhancing the rubbing performance. Moreover, sincefailure of the rubbing roller is a primary cause of rubbing rate decay,conditioning of the rubbing roller can help lengthen the roller lifetimein the rubbing process and increase the rubbing rate.

Therefore, the present invention provides the rubbing roller incombination with the conditioning roller, in order to improve rubbingquality and enhance rubbing performance. By employing the conditioningroller along with the rubbing roller, the rubbing process includes anextra conditioning step for conditioning the rubbing roller. Theconditioning step can lengthen the lifetime of the rubbing roller, sothat the rubbing roller do not have to be replaced too often, thusshortening the production cycle time and increasing the throughput.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A method for manufacturing a liquid crystal display device, saidmethod comprising: a first step of transporting a liquid crystal displaysubstrate under a rubbing apparatus comprising a rotating first rollingapparatus and a rotating second rolling apparatus arranged aside to thefirst rolling apparatus, the liquid crystal display substrate having analignment layer thereon, the first rolling apparatus having a rubbingcloth on a surface of the first rolling apparatus, wherein a surface ofthe rubbing cloth has a plurality of first pile fibers, so that thealignment layer is rubbed by the first pile fibers during rotation ofthe first rolling apparatus, the second rolling apparatus having aconditioning cloth on a surface of the second rolling apparatus, whereina surface of the conditioning cloth has a plurality of second pilefibers, so that the second pile fibers of the conditioning cloth on thesecond rolling apparatus are in contact with the first pile fibers ofthe rubbing cloth on the first rolling apparatus, and wherein the firstrolling apparatus rotates in a first rotating direction opposite to asecond rotating direction in which the second rolling apparatus rotates;a second step of binding a pair of substrates to each other, at leastone of the pair of substrates having gone through rubbing in the firststep; and a third step of injecting liquid crystal between thesubstrates.
 2. The method of claim 1, wherein if the second rollingapparatus rotates clockwise, the first rolling apparatus rotatescounter-clockwise.
 3. The method of claim 1, wherein if the secondrolling apparatus rotates counter-clockwise, the first rolling apparatusrotates clockwise.
 4. The method of claim 1, wherein the second rotatingspeed of the second rolling apparatus is faster than the first rotatingspeed of the first rolling apparatus.
 5. The method of claim 1, whereinthe rubbing apparatus further comprises a cover plate under the secondrolling apparatus and above the liquid crystal display substrate toprevent the second rolling apparatus in contact with the substrate.